In the last twenty years microprocessor speed has increased by several orders of magnitude and Digital Signal Processors (DSPs) have become ubiquitous. As a result, it has become feasible and attractive to transition from analog communication to digital communication. Digital communication offers the advantage of being able to utilize bandwidth more efficiently and allows for error correcting techniques to be used. Thus, by using digital communication, one can send more information through an allocated spectrum space and send the information more reliably. Digital communication can use wireless links (e.g., radio frequency) or physical network media (e.g., fiber optics, copper networks).
Digital communication can be used for transmitting and receiving different types of data, such as audio data (e.g., speech), video data (e.g., still images or moving images) or telemetry. For audio communications, various standards have been developed, and many of those standards rely upon frame based coding in which, for example, high quality audio is encoded and decoded using audio frames (e.g., 20 millisecond frames containing information that describes the audio that occurs during the 20 milliseconds). For certain wireless systems, audio coding standards have evolved that use sequentially mixed time domain coding and frequency domain coding. Time domain coding is typically used when the source audio is voice and typically involves the use of CELP (code excited linear prediction) based analysis-by-synthesis coding. Frequency domain coding is typically used for such non-voice sources such as music and is typically based on quantization of MDCT (modified discrete cosine transform) coefficients. Frequency domain coding is also referred to “transform domain coding.” During transmission, a mixed time domain and transform domain signal may experience a frame loss. When a device receiving the signal decodes the signal, the device will encounter the portion of the signal having the frame loss, and may request that the transmitter resend the signal. Alternatively, the receiving device may attempt to recover the lost frame. Frame loss recovery techniques typically use information from frames in the signal that occur before and after the lost frame to construct a replacement frame.
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